Four firms are on the shortlist for the £20 million second phase of refurbishment at the Whitgift shopping centre in Croydon, Surrey.Costain, Higgs and Hill, Laing and Tarmac have received tender documents from project manager E C Harris. Keen prices will be returned by all the firms but the key to winning the job lies in the method for successfully keeping the shopping centre open while the wholesale revamp takes place.They were shortlisted, from about 20 hopefuls, on the strength of their experience of refurbishing shopping centres without upsetting trade.Higgs and Hill has already got its foot in the door with a £900,000 enabling contract. The firm is installing fire detection and sprinkler systems under a six-month contract which started last month.Tender documents for the main contract are due to be returned this month, though interim interviews will take place. It is intended to name the winning contractor only three days after the tender documents have been returned.However, work is not scheduled to start until February next year, after the Christmas and New Year shopping sprees. Completion is in 27 months.The contract, under JCT terms, includes extending the shopping space and covering the malls with a steel-framed glazed enclosure. Lifts and escalators will be replaced and all pavings refurbished. A pub will be relocated to make way for a small office block and retail units.The refurbishment was designed by architect Covell Matthews Wheatley for client BZW/Whitgift Foundation.